Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $73.99   3.103%   $76.2859   $76.29   $76.30   $76.30  
  Purchase #2 $217.78   12.408%   $244.8021   $244.80   $244.80   $244.80  
  Purchase #3 $139.99   11.592%   $156.2176   $156.22   $156.20   $156.20  
  Purchase #4 $55.26   3.475%   $57.1803   $57.18   $57.20   $57.20  
  Purchase #5 $14.64   7.549%   $15.7452   $15.75   $15.75   $15.70  
  Purchase #6 $55.45   8.641%   $60.2414   $60.24   $60.25   $60.20  
  Purchase #7 $133.92   12.486%   $150.6413   $150.64   $150.65   $150.60  
  7 purchase totals = $691.03       $761.1138   $761.12   $761.15   $761.00